Method for desulphurating a nox-storage catalyst that is arranged in an exhaust channel of a combustion engine

A process for the desulfurization of at least one NOx storage catalytic converter arranged in an exhaust pipe of an internal-combustion engine, comprising the steps of:

• setting a minimum desulfurization temperature at the NOx storage catalytic converter and an operating mode of the internal-combustion engine with lambda<1;
• at least temporarily influencing one operating parameter of the internal combustion engine in order to reach at least one of the operating mode and the minimum temperature;
• initiating the desulfurization
• as a function of a ratio of the NOx concentration upstream and downstream of the NOx storage catalytic converter as a function of an NOx mass incorporated in the NOx storage catalytic converter (degree of sulfurization), and
• as a function of at least one of a current lambda value and a current temperature of the NOx storage catalytic converter;
• wherein the need for desulfurization is assessed continuously or in a stepwise manner on the basis of the degree of sulfurization and at least one of the current lambda value and the current temperature of the NOx storage catalytic converter;
• and
• wherein a threshold value for the degree of sulfurization at which desulfurization is initiated is varied continuously or in a stepwise manner as a function of at least one of the current lambda value and the current temperature of the NOx storage catalytic converter.